Field
The invention relates to over-the-air testing of a device in an anechoic chamber.
Description of the Related Art
When a radio frequency signal is transmitted from a transmitter to a receiver, the signal propagates in a radio channel along one or more paths having different angles of arrivals, signal delays, polarizations and powers. Also a frequency may change due to the Doppler effect which may cause variation in signal strength and fadings of different durations in the received signal. The transmitter and the receiver are not ideal either. In addition, noise and interference due to other transmitters interfere with the radio connection.
A transmitter and a receiver can be tested using a radio channel emulator emulating real circumstances. In a digital radio channel emulator, a radio channel is usually modelled with an FIR filter (Finite Impulse Response). A traditional radio channel emulation test is performed via a conducted connection such that a transmitter and a receiver are coupled together via at least one cable.
Communication between a DUT (Device Under Test) and a base station of a radio system can be tested using an OTA (Over The Air) test, where a real DUT, such a subscriber terminal, is surrounded by a plurality of antennas of an emulator in an anechoic chamber. The emulator may be coupled to or act as a base station and emulate propagation paths between the subscriber terminal and the base station according to a channel model by generating independent Rayleigh faded signals, for example. An antenna or a combination of antennas transmits the independently pre-faded communication signals to the DUT on the basis of weights determined by the emulated radio channel. However, the formation of weights and thus signals transmitted by the antennas have their specific limits and hence there is need for a new approach.